Cut-off valve



No. 12,966. PATBNTED MAY 29,l 1855.

D. STODDART.

CUT-OFF VALVE.

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UNITED STATES PATENT OFFICE.

DAVID STODDART, OF CINCINNATI, OHIO.

CUT-OFF VALVE.

Specification of Letters Patent No. 12,966, dated May 29, 1855.

To all whom it may concern.'

Be it known that I, DAVID STODDART, of

, Cincinnati, in the county of Hamilton and State of Ohio, have inventeda new and Improved lIode of Arranging and Operating Cut-Off Valves; andI do hereby declare that the following is a full and exact descriptionthereof, reference being had to the accompanying drawings and to theletters of reference marked thereon.

The nature of my invention consists yin so arranging a disk or piston,connected to the cut-oftl valve, and connecting the space below saiddisk or piston to the main cylinder, by a pipe or passage that thecut-off valve may be operated by the steam from the cylinder, passingand returning through said pipe or passage communicating with the spacebelow the said disk.

Description-The principle of this invention is susceptible of use inseveral forms with different constructive details, butthe onerepresented in drawings Nos. 8 and 4, we should prefer as the simplestand most generally applicable. These drawings represent a commonglobe-valve internally the same as in common use, but externally withthe additions of a small cylinder with a steam-tight piston or disk init, connected by cross-heads, and side-rods, to the valve stem. P thedisk (dotted in). H, H cross heads. R, R side-rods. S valve stem. Thespace in the small cylinder under P had no connection with the inside ofthe globe, but is connected by a pipe to some part of the cylinder, sayat the center for the present purpose of description. The disk P shouldhave a greater area than the cut-off valve.

Operation: The steam connection from the boiler to the engine beingopened, the main piston commences its stroke, and continues till itpasses the hole midway in the cylinder connecting to the space under P,then the steam behind the piston rushes through the connecting pipe andacting on disk P closes the valve, while the main piston continues tothe end of the stroke, the steam behind it and also under P, by reasonof expansion, having gradually reduced to nearly one-half its initialpressure. But if the area of P is sufficiently large the reducedpressure will still hold the valve shut, until the engine exhausts, whenthe steam under P will rush back again to the cylinder, leavingunbalanced the pressure of steam above the cut-off valve exerted on itsface, and hence the cut-off valve opens to give the engine steam for thereturn stroke when the like operation is again performed. In condensingengines the external atmospheric pressure on P will likewise air thevalve in opening. The part of either stroke performed before the steamconnection is opened between cylinder and disk P is equal one-half thestroke plus one-half depth of the main piston, and this latter item musthave due consideration in locating any other holes in the cylinder forcut-0E purposes. It is apparent that connections of cylinder to spacebelow disk P may be formed earlier in the stroke than already described,and the operation would be the same, except that a steam connection ofthe parts of the cylinder before and behind the piston would result insuch case, unless we insert in the connecting pipe a double-check-valveas shown in drawing No. 5, wherein if steam comes from one end of thecylinder through m as the arrow represents, it will shut the check valveopposite and continue through the branch o to the cut-off; or if steamcomes through m from the other end of the cylinder it will shut thedouble-check-valve on the opposite side, and continue to the cutoarrangement as before. Thus we might have a cut-oif changeable atpleasure, by several stop cocks and connecting pipes and opening a cockon each side of half stroke the engine will cut off after passing thefirst open cock. The distance between any point of cutting off and itscorresponding hole in the cylinder will vary with any -change in thesize or throttling of the hole or connecting pipe, in the pressure ofsteam, or speed of the piston. Where the hole and connections areproportionally large, and the motion of the piston slow, the valve willcut-o almost immediately as the main piston passes the hole, but as youdecrease the size of connection, quicken the speed of the piston andreduce the pressure of steam, so will the distance increase between thehole and the piston of the main piston, when the cut-o valve is fullyshut. A large connection will shut the valve quickly, but slamming isthe consequence which can be obviated in such case by the use of thedisk-pot or other contrivance already in use for like purposes. Eachcase must be determined by its own required conditions, according toestablished rules of philosophy7 and practice applicable in such cases.AAlso in assuming the proper ratio for the area of disk P, and thecut-orf valve, the period of cutting ofi' and the probable throttling ofsteam by the throttle or governor valve Inust enter into thecalculation.

Drawing No. l, represents section f of steam chest and part of cylinderof a coin- I'non slide valve engine with another construction of cut-offP and 29 disks O15-36 and 25 sq. in. area V valve of 36 sq. in. Oopening connecting to cylinder. The operation by the admission andexhaust of steain through opening O is substantially as alreadydescribed.

Drawing No. 2, shows another construction of cut-off with throttlecombined P annular piston or disk, F follower, G gland, p 29 p spacesfor packing, Y, cylindrical JOHN VAN AMRINGE, ELIZA J. STODDART.

